While reading MaxPF's CTD build tread, I noticed he uses stainless steel bolts on his exhaust manifolds. I would like to use new hardware on my exhaust manifolds and I am thinking of using stainless steel.

Anyone see any issues with this? Is there a special type of stainless that needs to be used?


Here is MaxPF's response to someone questioning the use of stainless steel bolts;

Quote:
Also, I would very strongly suggest you pull out those stainless bolts and replace them with regular g8 steel. I have been down this road too and I can tell you it can be a nightmare. Stainless will gald after many heat cycles and you an have a mess on your hands. The antiseize will help, but still not a good idea on exhaust stuff. They snap so easily.
Interesting, since my experience has been the exact opposite. I have found that once alloy steel bolts (i.e. Grade 5,8 or metric 8.8,10.9) have gotten hot enough in an exhaust system they will often seize in their holes, and they end up having about as much strength as a Grade 2 bolt (if that) so they will twist off with very little effort. Anti-seize helps with later removal, but they still rust badly and have a tendency to lose their threads because they get so soft. Stainless pretty much maintains it's strength, and I haven't seen it have any tendency to gall. Then again, I always use anti-seize on exhaust bolts.

A good example are the headpipe bolts screwed into the manifolds of the 6.2 I just removed. When I installed that engine I used stainless steel bolts with anti-seize to hold the flanges onto the manifolds (one rusted alloy steel stud on one manifold and two on the other had broken during removal of the pipes in the original install). When I went to remove them yesterday they broke loose with the same approximate force as I had tightened them with and cleanly unscrewed from the manifolds. They were discolored from the heat, but none the worse for wear. I have never had a steel manifold flange bolt be that easy to remove even after only a month of use.

An example of the perils of alloy steel bolts is the 12mm exhaust manifold bolt my friend Brian broke off in the head of his 12V while trying to remove it with a 3/8" drive ratchet, or the 2 12mm turbo mount studs I broke off (and had to extract by TIG welding a nut to them) with a regular box end wrench. The bolts had become so soft it felt like I was twisting off aluminum. Anyone who has removed many exhaust fasteners knows exactly what I am talking about.

I used grade 8 studs, stainless doesn't seem like a good idea as said.

There are different grades of stainless. Most of the stuff you can get at the hardware store is low grade stuff I wouldn't use but I have been using ARP stainless bolts on exhaust manifolds for a while and never had a problem with them. They are stronger than the hardware grade 8 bolts and they look real nice.

The other factor I see is that the original 6.2 exhaust manifold to cylinder head bolts were spec'd to be and interference fit thread. This slight interference helped them stay tight. When removing them, you can feel the difference if somone has lost one and replaced it with a regular thread metric bolt. The original bolts come out hard all the way, apparently for good reason.